SEISMOLOGICAL INVESTIGATIONS 267 



on account of the introduction of a new way of operating these instruments. 

 Details will be found in Lee's Memoir. 



The Wood- Anderson seismographs, which are adjusted with a period 

 of 2^ seconds, record the horizontal components of the earth's movement. 

 An instrument with about the same period to record the vertical component 

 is required. An experimental seismograph of this type was constructed in 

 the Observatory workshop and has been in operation for some months. 

 The special feature is the introduction of * viscous coupling ' (by means of 

 a plunger working in a cup filled with liquid) between pendulum and 

 mirror. Some promising records have been obtained from recent earth- 

 quakes, but modifications to the instrument will be required before 

 operation is entirely satisfactory. 



A paper by Dr. Lee, ' The travel-times of the seismic waves P and S, 

 a study of data from the International Seismological Summary, 1930 and 

 193 1,' is being published shortly as a Geophysical Memoir of the Meteoro- 

 logical Office. 



Seismology in the West Indies. 



The series of earthquakes which occurred in 1934 and 1935 in Montserrat 

 led to the despatch of an expedition to that island. Valuable reports on 

 the geological structure of the island and on the distribution of the earth- 

 quake centres were written by Mr. A. G. Macgregor and Dr. C. F. Powell. 

 The Wiechert seismograph and eight Jaggar shock recorders are still in 

 operation in the care of Mr. Kelsick, who is making regular reports on the 

 seismic activity in that island and is also collecting information about shocks 

 which are felt in other islands. From August to November 1937 about 

 forty earthquakes were reported by observers in Dominica. The Royal 

 Society has nominated a West Indies Seismological Committee, and this 

 Committee has under consideration the despatch of an expedition to 

 Dominica. The earthquakes in that island have been less frequent, how- 

 ever, in recent months, and the proposal is therefore in abeyance at present. 



The International Seismological Summary. 

 A Note by J. S. Hughes. 



The International Seismological Summary has now been prepared in 

 manuscript as far as July 1933 ; January, February and March are in the 

 press, while April, May and June are in process of being finally checked 

 through. 



The number of earthquakes dealt with in a given period of time remains 

 roughly constant but with a fluctuation which is mainly dependent on the 

 presence or absence of cases in which a long sequence of after-shocks to 

 an earthquake of great intensity occurs in a region well equipped with re- 

 cording stations. Such a case was provided by the Sunriku earthquake of 

 March 2, 1933, origin 39-1° N., 144-7° E., off the east coast of Japan. 

 This earthquake, which is notorious for the devastating tunami it produced, 

 was followed by a large number of shocks from the same neighbourhood, 

 but apparently not from a single focus. This interesting series of shocks was 

 worked out in as much detail as possible and a number of different epicentres 

 were determined. It is not claimed, however, that finality has been attained, 

 and the observations, extending over many days, would afford a good subject 

 for special study. Of the earthquakes listed for the month of March 1933, 

 142 were after-shocks of the series in question. 



